An off gas purification system provides superior results to other systems for the recovery of volatile organic compounds and the cleansing of output air that is free of detectable volatile organic compounds. Off gas is extracted from a source of off gas, followed by steps of compression and condensation. Compression and condensation produce liquid condensates and an off gas that must be further treated to produce pollutant-free exhaust. A separation device removes VOCs from the compressed air stream and returns those VOCs to the front of the system. The system emits discharge air that is free of any and all detectable volatile organic compounds per EPA's TO-15 method of sampling and analysis. Discharge air may be routed through conventional scrubbers or filters as a failsafe in case of system failure, as prescribed by environmental regulation. Prior to discharge, cleansed air may be heated and returned to the source of the off gas to thermally enhance desorption of remaining volatile organic compounds, wherein the vacuum pulsation of the off gas purification system creates differential pressure gradients in the source of the off gas which further improves VOC desorption and removal. Cleansed heated air may be concurrently returned to the separation device to thermally enhance desorption of volatile organic compounds. Cleansed air may be concentrated into one or several gas varieties prior to heating and routing.